Hi david,
i found the link below, uses split dowels i imagine a smidge under the id of the tube, won't help with the angle from the point of the drill between the two internal sizes but it might work.
Might work, worth a try maybe. Next time i have ago and i think i will do what the article says.
It is difficult though but worth persevering with as they are good i think.
Forgive my ignorance about plastics but is bought acrylic rod the same stuff as the water clear casting resin ? thats what i used.
http://www.thogamecalls.com/PDF%20Tutorials/WorkingWithAcrylic.pdf
Regards
Pete